With the advent of graphical user interfaces, the utilization of pointing devices with computers has become commonplace. Most computers today include a pointing device. The pointing device permits a user of the computer to control the movement of a pointer on the screen of the computer. Having the ability to control the pointer is necessary for activities such as selecting a window on the screen, highlighting text in a word processing program, etc. Typical pointing devices include a mouse, a touch pad, a joy stick, a wheel, and a trackball.
However, pointing devices are usually relative positioning devices. This means that the actual physical position of a mouse pointing device on a mouse pad, for example, has no bearing on the location of the pointer on the screen. The mouse instead transmits directional change information. A user moving the mouse a given distance to the right causes the computer to move the pointer on the screen a corresponding distance to the right. That the user moved the mouse from the left side of the mouse pad to the center of the mouse pad, for example, is no different than if the user had moved the mouse from the center of the mouse pad to the right side of the mouse pad.
This type of mouse pointing device is inherently a relative positioning device. In the case where the mouse pointing device is a mechanical mouse, the mouse includes two wheels which sense the relative change in position of the mouse along each of two axes. These wheels are incapable of detecting the absolute position of the mouse. In the case where the mouse is an optical mouse, the mouse includes an optical sensor that detects the number of lines of a grid over which the mouse has been moved, in each of two perpendicular directions. The optical sensor is also incapable of detecting absolute position of the mouse.
As a further example, joystick pointing devices are also typically relative positioning devices. When the control stick of a joystick is in its center position, this does not mean that the pointer on the screen of a computer is located in the center of the screen, but rather that the pointer is not moving on the screen. That is, the location of the control stick within its range of motion has no bearing on the location of the pointer on the screen. A user pushing the control stick to the left causes the computer to move the pointer on the screen a corresponding distance to the left. When the user lets up on the control stick the pointer stops to where it has last moved, and does not return to the center of the screen.
This type of joystick is also inherently a relative positioning device. In the case of one common type of joystick, pushing the control stick of the joystick in any of eight directions causes an electrical connection to be made on one of eight terminals evenly spaced around the control stick. This electrical connection is signaled to the computer to which the joystick is coupled; by identifying which terminal at which the electrical connection has been made, the computer is able to identify the direction in which the stick has been pushed. These terminals render the joystick incapable of detecting absolute position of the control stick within its range of motion.
Therefore, there is a need for a pointing device that has absolute positioning capability. Such a mouse pointing device should signal the computer to which it is coupled the location of the mouse on a mouse pad. Such a joystick pointing device should signal the computer to which it is coupled the location of the control stick of the joystick within its range of motion.